Electric motor with field assemblies having core pieces with mating features

ABSTRACT

An electric motor has a field assembly, such as a stator, has field coils that are wound to a net shape. Lead wires are brought out from the ends of each field coil. The field coils are insulated. The field coils are assembled with stator core pieces, such as pole pieces and return path pieces, into the stator. The stator core pieces are formed prior to being assembled with the field coils. In an aspect of the invention, the pole pieces and return path pieces are separately formed and then assembled together with the field coils, which have also been separately formed. The pole pieces and return path pieces are formed with mating features that are mated to hold the pole pieces and return path pieces together.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Nos.60/500,384, filed on Sep. 5, 2003, and 60/546,243 filed on Feb. 20,2004. The disclosures of the above applications are incorporated hereinby reference.

FIELD OF THE INVENTION

The present invention relates to dynamoelectric machines, and moreparticularly, to fields for dynamoelectric machines and methods ofmaking them.

BACKGROUND OF THE INVENTION

Dynamoelectric machines are machines that generate electric power or useelectric power. Common types of dynamoelectric machines are alternators,generators, and electric motors.

Electric motors are used in a wide variety of applications involvingpower tools such as drills, saws, sanding and grinding devices, and yardtools such as edgers and trimmers, just to name a few such tools. Thesedevices all make use of electric motors having an armature and a field,such as a stator.

FIG. 1 shows a typical prior art stator 100 for an electric motor.Stator 100 is formed from a lamination stack 102 around which aplurality of windings of magnet wires 104 are wound to form field coils114. Lamination stack 102 is formed by stacking together an appropriatenumber of individual laminations 108 and welding them together. Theindividual laminations 108 are typically made by stamping them fromsteel. To do so, loose laminations 108 are loaded in a stacker. Thestacker picks up the appropriate number of laminations 108 and placesthem in a fixture where they are welded together. The laminations 108are formed with slots so the resulting lamination stack 102 has slots110 therein in which the magnet wires 104 are wound. Magnet wires, asthat term is commonly understood, are wires of the type conventionallyused to wind coils in electric machines, such as armatures and stators.Prior to winding the magnet wires 104, insulating sleeves or insulatingslot liners (not shown), such as vulcanized fiber, are placed in theslots 110 and end rings 112 placed on the lamination stack 102. Endrings 112 are illustratively made of plastic and formed to include coilforms 116. Field coils 114 are then wound by winding the magnet wires104 in the slots 110. After the field coils 114 are wound, the end ofthe magnet wires 104 are appropriately terminated, such as to terminals118 in a terminal post 120. The magnet wires 104 are then bondedtogether, such as by the application of heat when bondable magnet wiresare used. Bondable magnet wires are magnet wires layered with a heatactivated thermoplastic or thermoset polymer adhesive. One type ofbondable magnet wires commonly used is wire available under the tradename BONDEZE from Phelps Dodge of Fort Wayne, Ind. Alternatively, themagnet wires 104 may be bonded by a trickle resin process describedbelow. Where the stator 100 will be used in an application that exposesit to a particularly abrasive environment, such as a grinder, an epoxycoating is applied to the field coils 114 for abrasion protection.

There are a number of problem areas in the process just described. Firstof all, it is a capital intensive process. To tool a line to make astator for a fractional horsepower motor that has a six second cycletime typically requires an investment in the three to five milliondollar range. The insulating slot liners must be positioned correctly tomeet U.L. (Underwriters Laboratories) requirements and kept positionedproperly. In the existing process, the paper slot liners can move whenthe stator moves to the next station in the process.

The end ring limits slot fill. Slot fill is the amount of magnet wiresthat can be placed in the slots. The greater the slot fill, the higherthe magnetic field generated by the stator. However, increasing theamount of magnet wires placed in the slots can cause the end ring todeform. The end ring can be thickened to reinforce it, but this reducesthe slot volume available for the magnet wires.

In the manufacturing process for the stator described above, once themagnet wires have been wound in the slots and the ends of the magnetwires terminated, the magnet wires are bonded if bondable wire is beingused and a “trickle” resin is applied over the magnet wires if trickleresin is being used. The process of applying the trickle resin is asomewhat difficult process to manage to obtain consistent results. Italso has a number of drawbacks, not the least of which is the cost anddifficulty of performing it with reliable, consistent results.

Initially, the trickle process requires the use of a relatively largeand expensive oven to carefully preheat the partially assembled statorsto relatively precise temperatures before the trickle resin can beapplied. The temperature of the trickle resin also needs to be carefullycontrolled to achieve satisfactory flow of the resin through the slotsin the lamination stack. It has proven to be extremely difficult toachieve consistent, complete flow of the trickle resin through the slotsin the lamination stack. As such, it is difficult to achieve good flowbetween the magnet wires with the trickle resin. A cooling period mustthen be allowed during which air is typically forced over the stators tocool them before the next manufacturing step is taken. Furthercomplicating the manufacturing process is that the trickle resintypically has a:short shelf life, and therefore must be used within arelatively short period of time. This requires that batches of thetrickle resin be mixed frequently with any that isn't used within itsshelf life wasted.

The end result is that stators must often be designed for the process asopposed to optimum performance and cost.

SUMMARY OF THE INVENTION

In an aspect of the invention, a field assembly, such as a stator, for adynamoelectric machine made in accordance with an aspect of theinvention has field coils that are wound to a net shape. Lead wires arebrought out from the ends of each field coil. The field coils areinsulated. The field coils are assembled with stator core pieces, suchas pole pieces and return path pieces, into the stator. The stator corepieces are formed prior to being assembled with the field coils. In anaspect of the invention, the pole pieces and return path pieces areseparately formed and then assembled together with the field coils,which have also been separately formed. The pole pieces and return pathpieces are formed with mating features that are mated to hold the polepieces and return path pieces together.

In an aspect of the invention, the mating features include each returnpath piece having a projection extending from each end and each polepiece has a neck with opposed receiving pockets therein between opposedfingers. Each opposed receiving pocket in a pole piece neck receives theprojection at one of the ends of one of the return path pieces.

In an aspect of the invention, the dynamoelectric machine is an electricmotor. In an aspect of the invention, a hand-held power tool has such anelectric motor.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a perspective view of a prior art stator;

FIG. 2 is a flow chart of a method for forming a stator in accordancewith an aspect of the invention;

FIG. 3 is an exploded assembly view of a stator formed in accordancewith the method of FIG. 2;

FIG. 3A is a perspective view of a slot liner;

FIG. 3B is a top view of an electric motor made using the stator of FIG.3;

FIGS. 4A–4C are perspective views of a stator being assembled inaccordance with an aspect of this invention;

FIGS. 5A–5E are side section views of stator return path and pole pieceswith mating features in accordance with an aspect of this invention;

FIG. 5F is a side section view of a pole piece and field coil withportions of the pole piece staked over the field coil;

FIGS. 6A–6C are perspective views of a mold used to encapsulate a fieldcoil in accordance with an aspect of the invention, a coil prior tomolding and a field coil after molding;

FIGS. 7A and 7B are side section views of a variation of the stator ofFIG. 4 in accordance with an aspect of the invention;

FIG. 8 is a cross-section of a power tool having a stator in accordancewith an aspect of the invention;

FIG. 9 is a front perspective view of an insulating sleeve forinsulating field coils of a stator in accordance with an embodiment ofthe invention;

FIG. 10 is a rear perspective view of the insulating sleeve of FIG. 9;

FIG. 11 is a perspective view of a field coil/insulating sleeve assemblyusing the insulating sleeves of FIGS. 9 and 10;

FIG. 12 is a perspective view of the field coil/insulating sleeveassembly of FIG. 11 assembled on a pole piece;

FIG. 13 is a perspective view of an insulating slot liner in accordancewith an embodiment of the invention;

FIG. 14 is a side view of the insulating slot liner of FIG. 13;

FIG. 15 is a cross-sectional view of a stator in accordance with anembodiment of the invention in which field coils are insulated by theinsulating slot liner of FIGS. 13 and 14;

FIGS. 16A and 16B are side and front view of an insulating slot liner inaccordance with an embodiment of the invention that is a variation ofthe insulating slot liner of FIGS. 13 and 14;

FIG. 17 is four pole stator formed in accordance with an embodiment ofthe invention;

FIG. 18 is a perspective view of a variation of the insulating sleeve ofFIG. 9;

FIG. 19 is a side section view of stator core pieces having a coating ofinsulation;

FIG. 20 is an isometric view of an insulating slot liner made of a layerof insulation material with a B-stage thermoset adhesive or athermoplastic thereon;

FIG. 21 is a side view of a field coil insulated with the insulatingslot liner of FIG. 20; and

FIG. 22 is a perspective view of a field having the field coil of FIG.21.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS.

The following description of the preferred embodiment(s) is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses.

Referring to FIGS. 2 and 3, a process for making a field assembly,stator 300 in this instance, in accordance with an aspect of theinvention is shown. At step 210, a coil, such as coil 614 (FIG. 6), forfield coils 304 of stator 300 is wound to a predetermined shape,preferably net shape, by winding magnet wires 303 to the predeterminedshape. “Net shape” means the final shape of the field coils 304 in anassembled stator 300. At step 212, the magnet wires 303 are bondedtogether. The magnet wires 303 are preferably bondable magnet wires,such as BONDEZE wires, having a layer of heat activated thermoplastic orthermoset adhesive thereon and heat is applied to the formed coil 614 toactivate the adhesive on the magnet wires 303 to bond them together. Itshould be understood that the magnet wires can be bonded when the coilis still in the winding tooling or after it has been removed from thetooling. An advantage of bonding the wires when the coil is still in thewinding tooling is that it assures that the coil maintains its shapewhen it is removed from the tooling. The coils may also be compressedduring bonding. The bonded coil 614 is then tested at 213.

Field coils 304 have coil ends 305 with lead wires 302 extendingtherefrom which are brought out at step 214 from the formed coil 614.Lead wires 302 can be brought out using different alternatives. Coilends 305 may illustratively be terminated at terminals 307 and leadwires 302 attached to the terminals 307. Lead wires 302 can be attacheddirectly to coil ends 305. Lengths of coil ends 305 can be insulated byvarious methods, such as shrink tubing, various wall thickness TFE orPTFE tubing, and the insulated lengths provide the lead wires 302. Theuse of tubing, such as TFE or PTFE tubing, in addition to insulating thecoil ends 305, further provides the advantages of strain relief andadded rigidity to lead wires 302. Sliding tubing such as TFE or PTFEtubing over the coil ends 305 shields them and the tubing can beretained by any type of end termination.

At step 216, the formed coil 614 is insulated to form field coil 304.The formed coil 614 can be insulated by encapsulating it with anencapsulation material 309 that forms an encapsulation 313. Theencapsulation material 309 is illustratively an elastomericthermoplastic or thermoset plastic, such as thermoset liquid siliconrubber. Encapsulation material 309 is illustratively injection moldedaround field coils 304. It should be understood that other processes andmaterials can be used to encapsulate the formed and bonded coils withencapsulation material 309, such as transfer molding or spraying theencapsulation material 309. The encapsulation material could also be amore rigid thermoset. The encapsulation material may illustratively bethermally conductive and could also be a more rigid type of thermallyconductive plastic, such as a Konduit® thermoplastic commerciallyavailable from LNP Engineering Plastics of Exton, Pa. The encapsulationmaterial may illustratively be applied using the known vacuumimpregnation process. The formed field coil 614 would be placed in avacuum chamber and the encapsulation material wicks onto the field coil614.

Encapsulating the field coils 304 with the appropriate encapsulatingmaterial enhances abrasion protection and improves tracking resistance.Some types of power tools, such as grinders that are used to grind metaland remove mortar between bricks (called tuck pointing), generate a lotof abrasive particles that are drawn into the motor during operation andthus pass over the stator and rotor coil windings. These particlesabrade the insulation of the wire, and also tends to abrade the extratrickle varnishes or slurries that may be used to coat the coilwindings. Eventually, the wires electrically short and the motor burnsup, resulting in an inoperable power tool. Tracking is a condition wherean alternate conductive path is created outside the motor, thus carryingelectrical current where it normally doesn't go, such as outside of themotor windings. This path is normally created by metal debris drawinginto the motor during operation of the power tool that collects in thetool housing and contacts exposed elements of the electrical system ofthe power tool, such as brush boxes, exposed motor field windings, andlead wires.

Silicon rubber, such as liquid silicon rubber, is one such encapsulatingmaterial that can be used to enhance abrasion protection and improvetracking resistance. Silicon rubber is an elastomeric material andcushions the particles drawn into the motor when the particles impactit. Using a grade of silicon rubber with an appropriate durometer givesa desirable balance of functionality in terms of mechanical strength,abrasion resistance, tear resistance, and manufacturability.Illustratively, the liquid silicon rubber has a durometer in the rangeof 40 to 70 Shore A, and illustratively greater than about 50, and ahigh tear strength, that is, a tear strength of 200 pounds per inch orgreater. It should be understood that other elastomers having comparableproperties can also be used as the encapsulating material. The siliconrubber, or similar elastomers, can be applied by various means inaddition to injection molding, such as spray-on, brush-on andcompression molding and can be cured by any appropriate method, such asheat cure, room temperature cure, moisture cure and UV light cure.

Alternatively or in addition to encapsulating the field coils,insulating slot liners, such as slot liner 322 (FIG. 3A), can be placedin the slots of the stator core between pole pieces 308 and innersurfaces of return path pieces 310. Such a slot 503 is shown morespecifically in the embodiment of FIG. 5A between pole pieces 404 and aninner surface 505 of return path pieces 402. The insulating slot linersmay illustratively be known types of insulating slot liners, such asthose made of vulcanized fiber or rag-polyester.

Insulated field coils 304 are assembled with stator core pieces 306 toform stator 300. Stator core pieces 306 include pole pieces 308 and backiron or return path pieces 310.

Stator core pieces 306 are formed at step 220 out of steel laminations,as discussed above. In this regard, the laminations can be stacked andbonded together, such as by welding, or the laminations 706 (FIGS. 7Aand 7B) stamped with interlocks, such as interlocks 704 (FIGS. 7A and7B), which interlock the laminations together as the laminations arestamped. Each-core piece 306 may illustratively be seam weldedseparately across its laminations to strengthen it during handling,assembly of stator 300 and during operation of the motor in which stator300 is used. Stator core pieces 306 can also be made by molding orpressing them out of an iron powder, illustratively, insulated ironpowder, such as a sulfate coated iron powder. One such sulfate coatediron powder is SOMALOY™ 500 available from Höganäs AB of Sweden throughits U.S. subsidiary, North American Höganäs, Inc., 111 Hoganas Way,Hollsopple, Pa. 15935-6416. It should be understood that stator corepieces 306 could also be formed from other iron powders that can bepressed or molded, such as sintered iron powder.

It should be understood that forming the stator core pieces 306 isillustratively carried out independently of forming field coils 304 andvice versa. Consequently, stator core pieces 306 and field coils 304 canbe made on separate lines and stockpiled until needed. It also allowsthe geometry of field coils 304 and stator core pieces 306 to beoptimized. Moreover, pole pieces 308 are illustratively made separatelyfrom return path pieces 310. This allows the geometry of the pole pieces308 and the return path pieces 310 to be separately optimized.Preferably, the pole pieces 308 are identical as are the return pathpieces 310 and the field coils 304.

Each pole piece 308 illustratively has a neck 311 with a rectangularouter base 312 with an inwardly opening arcuate cylindrical pole tipsection 314 thereon having pole tips 318. Each return path piece 310 isillustratively semi-cylindrical with opposed ends 316 shaped to attachto one or both of the opposed ends 316 of the other return path piece310 and the rectangular outer bases 312 of pole pieces 308. Inassembling encapsulated field coils 304 and stator core pieces 306,encapsulated field coils 304 are placed over the necks 311 of respectivepole pieces 308. Return path pieces 310 are then secured to pole pieces308, such as by snapping together, welding, riveting, with screws,forming operations, or the like.

An armature, such as armature 352 (FIG. 3B) is then placed in stator 300in making an electric motor, such as electric motor 350 (FIG. 3B).

The process just described provides a number of advantages. A relativelysimple, inexpensive machine can be used to wind the field coils 304.Moreover, multiple magnet wires can be wound at the same time to formthe field coils 304. It also provides for a higher slot fill factor(total area of wire in the winding slot, including wire insulation,divided by available or total area of the winding slot), particularlywhen the wires of the coils are compressed during bonding. Looked at adifferent way, it provides for denser field coil that has a higherpacking factor (total area of the wire, including wire insulation,divided by the area of the envelope of the field coil defined by theinner and outer perimeters of the field coil).

Compressing the wires during bonding improves bonding by assuring thatadjacent wires of the coil are firmly together resulting in increasedbond strength. Also, by pressing the wires of the coil together, many ofthe voids from the winding process are eliminated. This reduces oreliminates air pockets in the coil resulting in improved heat transferbecause the inner wires of the coil are in direct contact with the outerwires, which are exposed to airflow when the motor is in operation. Theresistive heat generated during operation of the motor can thus bedissipated through the coil quicker by being conducted through adjacentwires rather than convection through an air pocket. Finally, bycompressing the wires of the coil together, a higher slot fill factorand packing factor can be achieved compared to conventional windingtechniques. This allows for more turns of wire or equal turns of largergauge (thicker) wire than provided by conventional winding techniques.Field coils having packing factors of greater than sixty, seventy,eighty and up to about eighty five percent can be achieved with thisprocess.

In an aspect of the invention, multi-stranded wire is used to wind thefield coils 304 which also provides for more slot fill. A commerciallyavailable wire of this type is commonly known as litz wire.

In an aspect of the invention, multiple magnet wires having differentfunctions and, illustratively, different sizes, can be wound to form thefield coils 304. For example, eighteen gauge magnet wire can be wound ineach field coil 304 to form one or more coils that are energized toprovide the magnetic field that interacts with the armature of theelectric motor to rotate the armature. Twenty-one gauge wire can bewound in each of field coils 304 to form coils that are energized tobrake the armature. In this regard, the magnet wires of different sizesare wound sequentially, that is, first one size of magnet wire is woundand then the second size of magnet wire is wound, or they are wound atthe same time. The twenty-one gauge wire is illustratively wound withmore turns than the eighteen gauge wire to produce the needed amount offlux to brake the armature quickly.

Forming the field coils 304 into predetermined shape(s), such as bywinding them to pre-determined shape(s), and then bonding the magnetwires 303 allows the field coils 304 to be wound so that they extendbeyond edges 320 of pole tips 318 of pole pieces 308 when field coils304 are assembled in stator 300. That is, the field coils 304 can extendbeyond the edges 320 of pole tips 318 of pole pieces 308. In thisregard, the return path pieces 310 may be formed so that they areaxially longer than the pole pieces 308. This also allows the magnetwire to be wound so that the field coils 304 extend around or beyondends of the pole pieces 308 and not extend beyond the edges of thereturn path pieces 310 once they are assembled in stator 300. Also, thecoil forming step allows the field coils 304 to be formed morecompactly, as discussed, and thinner. By being able to form the fieldcoils 304 so that they extend beyond edges 320 of pole tips 318 of polepieces 308 and be more compact, applicants have determined that at leastten percent more output power can be achieved as well as providingbetter thermal characteristics for a given size field. For example,applicants found that an electric motor having a 59 mm diameter statormade in accordance with the invention has about thirty-six more percentoutput power than an electric motor having a 59 mm diameterconventionally made stator. This also permits a smaller diameter statorto be used for a given amount of output power. For example, applicantsfound that an electric motor having a 55 mm diameter stator formedaccording to the invention has about the same output power as anelectric motor having a 59 mm diameter conventionally formed stator.

Forming the field coils 304, illustratively into net shapes, and thenassembling the field coils to the pole pieces also allows the overalldiameter of stator 300 for a given diameter motor to be kept the samebut allows a larger diameter armature to be used. As is known, themaximum motor performance measured by cold or hot max watts outincreases as the size of the armature increases. More specifically, asthe diameter of a motor armature increases, the power of a motor goes upby the square of the armature diameter. But with conventional motors,every incremental increase in the diameter of the armature results in acorresponding increase in the diameter of the stator and thus of themotor. A motor using a stator made in accordance with the inventiondiscussed above and as further discussed below allows the windings ofthe field coils, such as field coils 304, to be packed more tightly. Italso allows them to be packed more thinly which in turn allows thethickness of the stator core pieces to be reduced. Packing the windingsof the field coils 304 thinner allows, as discussed above, the diameterof the motor to be reduced or a larger diameter armature used for agiven diameter motor. The above motor having a 55 mm diameter statorconstructed in accordance with this invention (which is also thediameter of the motor) for use in a small angle grinder provides a poweroutput of about 1000 W. To achieve a power output of 1000 W using aconventional stator requires a 59 mm stator.

Using the above referenced motor with the conventional 59 mm diameterstator as an example, which has field coils wound about the pole tips ofthe poles by a needle-winder as is conventional, this motor has a totalslot area for the field coils (slot area being the area in which thefield coils can be disposed which in the case of the conventional needlewound field is limited by the width or arc of the pole tips of thepoles) of about 90 mm² and radial dimensions as follows:

Armature radius: 17.5 mm Airgap  0.5 mm Field coil thickness:  6.5 mm(includes thickness of pole tip) Back iron thickness:   5 mm

(The air gap is the gap between the field coils or faces of the poletips, whichever is closer to the armature, and the armature.)

The above referenced motor with the 55 mm diameter stator made inaccordance with this invention where the field coils 304 can extendbeyond the edges 320 of the pole tips 318 has a total slot area for thefield coils of about 100 mm² with the following radial dimensions:

Armature radius 17.5 mm Airgap  0.5 mm Coil thickness  4.5 mm (includesthickness of pole tip) Back iron thickness   4 mm

The armature winding in both cases is eight turns of 0.52 mm wire andwinding of each field coil in both cases is sixty-two turns of 0.75 mmwire.

Alternatively, a 59 mm diameter stator constructed according to thisinvention could be used allowing for the diameter of the armature to beincreased 4 mm, with a commensurate increase in power.

Table 1 below shows the armature OD, Field OD, Armature OD/Field ODratio, and power output at 38,000 RPM for conventional AC motors havinga Field OD of 57 mm and 59 mm and Table 2 below shows the sameinformation for AC motors with fields made in accordance with theforegoing aspect of the invention having a field O.D. of 55 mm and 59mm.

TABLE 1 Field O.D. Armature O.D. Ratio RPM Watts 56.96 mm 35.19 mm 0.61838000  800 59.00 35.19 mm 0.596 38000 1000

TABLE 2 Field O.D. (D_(f)) Armature O.D. (D_(a)) Ratio RPM Watts 55.00mm 35.19 mm 0.640 38000 1050 59.00 37.00 mm 0.627 38000 1600

Referring to the AC motor having a 59 mm field O.D. as an example, ascan be seen from Tables 1 and 2, the motor made in accordance with theforegoing aspect of the invention allows use of a 37 mm O.D. armaturewith a commensurate increase in power to 1600 Watts at 38,000 RPMcompared to a conventional AC motor which utilizes a 35.19 mm O.D.armature and has a power output of 1000 Watts at 38,000 RPM. Also as canbe seen from Tables 1 and 2, a motor having a 55 mm O.D. field made inaccordance with this aspect of the invention allows use of a 35.19 mmO.D. armature resulting in a power output of 1050 Watts at 38,000 RPM,which is more than 1.25 times the power of an existing AC motor having a56.96 mm O.D. field which also uses a 35.19 mm O.D. armature. Inaccordance with the foregoing aspect of the invention, for a given motorvolume (motor outside diameter × motor length) an AC electric motor 350(FIG. 3B) made in accordance with the foregoing aspect of the inventionhas an armature 352 and a field or stator 300 with an armature O.D.(D_(a)) to field O.D. (D_(f)) ratio of at least 0.625 which results inmotor 350 having at least 1.3 times the power of an existing AC electricmotor with a field having the same O.D. but with the smaller O.D.armature. The motor is also thermally balanced with the operatingtemperature of the field being about the same as the operatingtemperature of the armature at the current or power rating of the motor,such as the Underwriter Laboratories' rating for the motor.

Forming the stator core pieces 306 separately from each other andparticularly from the field coils 304 decouples an important aspect ofthe design and configuration of the field coils from the design andconfiguration of the stator core pieces 306, the pole pieces 308 inparticular. In conventional stators with needle-wound field coils, thefield coils can't extend beyond the edges of the pole tips since thepole tips are used to hold the wires of the field coils during windingand before bonding or application of the trickle resin. The usable fieldwinding area is thus defined by the width or arc (included angle) of thepole tips. While the arc of the pole tips can be increased to increasethe area in which the field coils can be wound, this causes performanceproblems, particularly, commutation performance. Extending the arc ofthe pole tips too much degrades commutation. Thus, commutationperformance limits the degree to which the area in which the coils arewound can be increased by increasing the arc of the pole tips. Incontrast, in a stator made in accordance with the invention as describedabove and below, such as stator 300, the arc of the pole tips does notlimit the area in which the field coils can be disposed, and thus doesnot limit the size of the field coils 304. As discussed, the field coils304 can be formed so that they extend beyond the edges 320 of the poletips 318. That is, the arc or included angle of the field coil isgreater than the arc or included angle of the pole tips. Thus, in a twopole stator such as stator 300, the two field coils 304 can be formed sothat their respective edges are almost adjacent each other, that is,each field coil 304 has an arc (included angle) of almost one-hundredand eighty degrees, as shown representatively by field coils 614 in FIG.15. Comparing the above discussed 55 mm motor having a stator made inaccordance with this invention to the above discussed 59 mm motor havinga conventional needle-wound stator, the pole tips of the 55 mm motorhave an arc or included angle 710 (FIG. 7A) of 110 degrees and the fieldcoils have an arc or included angle 712 of 158 degrees, whereas thefield coils of the conventional 59 mm motor have an arc or includedangle of 125 degrees which is the arc or included angle of the poletips. Stators made in accordance with this invention can have fieldcoils that have arcs or included angles of that are more than 100% ofthe arcs or included angles of the pole tips and up to about 163% of thearcs or included angles of the pole tips, such as, by way of example andnot of limitation, at least 110%, 125%, 140%, 155% of the arcs orincluded angles of the pole tips.

Forming the field coils 304 before assembling them in stator 300 alsoprovides the advantage of simplifying “leading” them. “Leading” thefield coils 304 is the process of bringing out or attaching lead wires,such as lead wires 302. In conventional stators where the field coilsare needle-wound around the poles, a length of the magnet wire must bebrought out from the wound coil and either attached to a terminal placedin the end ring or if used as the lead wire, terminals attached. If themagnet wire is used as the lead wire, it must be strain relieved. Thisprocess typically results in a length of wire (magnet wire, lead wire,or both) that is longer than needed for the actual lead wire which mustthen be routed through the stator to secure it and keep it from touchingthe armature when the motor in which the stator is assembled in use. Incontrast, by forming field coils 304 separately from the stator corepieces 306 and before they are assembled in stator 300, the “leading”process is simplified as it is much easier to get access to the coilsince it is not in the stator. The lead wire can be attached directlyadjacent the coil with little magnet wire needed to be brought out fromthe coil. If the magnet wire is used as the lead wire, only the lengthneeded for the lead wire need be brought out. A further advantage isthat if an unrepairable mistake is made in “leading” the field coil 304,only that field coil 304 need be scrapped and it can be scrapped withoutany disassembly. In contrast, if a mistake is made in leading a fieldcoil in a conventional stator, either the entire stator has to bescrapped or the field coils disassembled from the stator and new fieldcoils wound, which is usually impractical if not impossible.

Pressing the stator core pieces 306 out of iron powder providesadditional advantages to those described above. The stator core pieces306, the pole pieces 308 in particular, can be formed in one operationas a three-dimensional part. In contrast, in the conventional processdescribed above, the pole pieces of the stator are made by stacking anappropriate number of laminations, in effect, stacking the appropriatenumber of two-dimensional pieces to arrive at the resultingthree-dimensional pole piece. By pressing the stator core pieces 306from iron powder, tighter tolerances can be maintained than with theconventional process.

Using insulated iron powder as the iron powder provides additionaladvantages in that insulated iron powder has low eddy current losses.

FIGS. 4A–4C show a variation of the above described aspect of theinvention. A field assembly, stator 400 in this instance, has first andsecond return path pieces 402, first and second pole pieces 404, andfirst and second field coils 406. Field coils 406 are illustrativelypre-formed coils encapsulated with an elastomeric encapsulation 408.Field coils 406 are illustratively wound to the predetermined shape asdescribed above with reference to the embodiment shown in FIG. 3.Illustratively, elastomeric encapsulation 408 is liquid silicon rubber,as described above. It should be understood that field coils 406 can beinsulated in other manners as described above.

To assemble stator 400, field coils 406 are placed over necks 414 ofpole pieces 404. Necks 414 have opposed receiving pockets 504 (FIGS.5A–5C) therein between pole tip section 522 of pole pieces 404 and baseportion 524 of necks 414 of pole pieces 404. Circumferentially andradially outer edges 526 of pole tip section 522 projectcircumferentially outwardly to provide lips 528 (in other words, poletip portions 522 have undercuts 527). Edges 526 may illustratively berecessed and have a radius as shown in FIG. 5D to ease the assembly offield coils 406 to pole pieces 404. If edges 526 are sharp edges, theinsulation on field coils 406 could catch and possibly be displaced fromits correct position on the coil. With edges 526 having a smooth radius,the insulation on field coils 406 more freely slides onto pole pieces404 and facilitates keeping the insulation correctly positioned on fieldcoils 406.

Field coils 406, when encapsulated with an elastomeric encapsulationmaterial such as liquid silicon rubber, snap over lips 528 and intoundercuts 527 which retains them in place during further assembly ofstator 400. Bumps or other interference features may illustratively beformed of the encapsulation material where the field coils abut the poletip portions 522 to further retain the field coils 406 to the polepieces. In a variation, lips 528 may also be staked over field coils 406in one or more places, shown illustratively at 529, to provide furtherretention of field coils 406 as shown in FIG. 5F.

Ends 418 of field coils 406 may extend beyond pole tips 420 of polepieces 404. Return path pieces 402 are then brought in radially(laterally) and mated to the pole pieces 404. Opposed edges 423 ofradial outer ends 422 of pole pieces 404 have mating features 424 thatmate with corresponding mating features 426 in edges 428 of return pathpieces 402, as described in more detail below.

In an aspect of the invention, field coils 406 may have mating features410 formed in encapsulation 408. Pole pieces 404 have correspondingmating features 412 formed therein, and in this regard, pole pieces 404may be encapsulated with an encapsulation material with the matingfeatures 412 formed in this encapsulation, or the mating features 412formed directly in the soft magnetic material of which pole pieces 404are made. Mating features 410 may illustratively be a projection ordetent and mating feature 412 would then be a corresponding hole orrecess. The converse could also be used—that is, mating feature 412 isthe projection or detent and mating feature 410 is the correspondinghole or recess. Mating features 410 of field coils 406 and matingfeatures 412 of pole pieces 404 mate together when field coils 406 areplaced over the necks 414 of pole pieces 404, holding each field coil406 to a respective pole piece 404, making coil/pole subassemblies 416.Pole pieces 404 may illustratively be made of laminations or of ironpowder, such as insulated iron powder, such as described above withreference to FIGS. 2 and 3. Similarly, return path pieces 402 can bemade of laminations or insulated iron powder.

Turning to FIGS. 5A and 5B, an embodiment of mating features 424, 426 isshown. Mating feature 426 of each edge 428 of each return path piece 402is a projection 500 that extends from the respective edge 428 of thereturn path piece 402, with a recess 502 at a junction of projection 500and edge 428 of return path piece 402. Mating feature 424 in eachopposed edge 423 of each radial outer end 422 of each pole piece 404(FIG. 4B) comprises receiving pocket 504 defined between outer finger506 of base portion 524 of pole piece 404 and pole tip portion 522 ofpole piece 404. Mating feature 424 further includes outer finger 506having a projection 510 extending radially inwardly from an outer end512 of finger 506.

Each receiving pocket 504 is illustratively larger than the projection500 of the respective return path piece 402 so that projection 500 iseasily received in the receiving pocket 504. This is accomplished byforming finger 506 so that it is at an angle 514 with respect toprojection 500, as shown in FIG. 5B, when projection 500 is firstinserted into receiving pocket 504. Additionally, mating radii ofreceiving projection 500 and receiving pocket 504 are sized so thatthere is always an appropriate clearance 516 between them takingtolerances into account.

Once the projections 500 of return path pieces 402 are inserted intoreceiving pockets 504 of respective pole pieces 404, the fingers 506 ofpole pieces 404 are deformed radially inwardly so that projections 510extending radially inwardly from outer ends 512 of fingers 506 arereceived in recesses 502 of respective return path pieces 402. Themating of projections 510 in recesses 502 forms mating detents 518 (FIG.5A) that mechanically lock pole pieces 404 and return path pieces 402together. Return path pieces 402 and pole pieces 404 are thusmechanically interlocked by mating detents 518 and held together byfriction. Pole pieces 404 can also be welded to return path pieces 402to further strengthen the attachment of pole pieces 404 to return pathpieces 402. Alternatively, pole pieces 404 and return path pieces 402could just be welded together.

FIG. 5C shows a variation of the mating features 424, 426 of FIGS. 5Aand 5B which is almost identical to the embodiment shown in FIGS. 5A and5B, and only the differences will be discussed. Elements of FIG. 5Ccommon with the elements of FIGS. 5A and 5B are identified with the samereference numbers. The difference is that the mating detent 518 is moveddistally outwardly along projection 500. This increases the “criticallength” designated by reference numeral 520 compared with the length ofthe same segment in the embodiment shown in FIGS. 5A and 5B. Thiscritical length is the length of the segment of return path piece 402and pole piece 404 through which the majority of the magnetic flux iscarried. Maximizing this critical length benefits motor performance.

Illustratively, when return path pieces 402 are mated with pole pieces404, they are brought together radially shown by arrow 440 in FIG. 4B,as opposed to axially. The return path piece 402 radially compressesrespective sides of the field coils 406 mounted on pole pieces 404. Thiseliminates the return path piece 402 sliding axially across the fieldcoils 406 and the possible damage to the insulation surrounding thefield coils 406 due to the return path piece 402 sliding across them.Also, the tolerances, particularly of the field coils 406, can besomewhat looser when the return path pieces 402 and pole pieces 404 aremated by bringing them together radially as opposed to axially.

Making the return path pieces 402 separately from the pole pieces 404also provides the advantage that not only can different materials, suchas different magnetic grades of steel, be used to make them, butdifferent construction techniques can be used. For example, the polepieces 404 could be made of stacks of laminations as described above andthe return path pieces made of solid steel. The pole pieces 404 wouldthen include deformable portions that would be deformed againstcorresponding portions of return path pieces 402 to fasten the returnpath pieces 402 and pole pieces 404 together.

While stators 300 and 400 (FIGS. 3 and 4) have been described in thecontext of having two poles with two return path pieces and two polepieces, it should be understood that other configurations can be usedthat are within the scope of the invention. For example, only one returnpath piece could be used, which would illustratively be a cylindricalpiece, with the two pole pieces being affixed to an inner side of thereturn path piece on opposite sides thereof. Each return path piececould be made of multiple pieces that are joined together, such as bywelding or by forming mating features therein that snap together. Thestator core pieces could also be held together by being inserted in astator housing. The stators could also have more than two poles, such asfour, six, eight or other multiples of two. In this regard, at least onepole piece would be provided for each pole and they would be spacedequidistantly around the stator. Each pole piece could be made ofmultiple pieces that are joined together.

FIG. 17 shows such a stator 1700 having more than two poles,illustratively, four poles. Stator 1700 illustratively includes fourreturn path pieces 1702, four pole pieces 1704 and four field coils1706. Return path pieces 1702, pole pieces 1704 and field coils 1706 areall separately formed in the manner described above. Field coils 1706are then placed over necks 1708 of pole pieces 1704 so that they abutpole tips 1710 of pole pieces 1704 and pole pieces 1704 and return pathpieces 1702 mated together.

In an aspect of the invention, the core pieces of the stator include atleast three pieces—two pole pieces and one return path piece. In anaspect of the invention, the pole pieces, return path piece or piecesand the field coils are all separately formed and then assembledtogether. By separately formed, it is meant that the pole pieces areformed separately from the return path piece or pieces which are in turnformed separately from the field coils.

FIG. 6 shows an illustrative embodiment of a mold 600 that can be usedto mold the encapsulation material, such as encapsulation material 309(FIG. 3) that forms the encapsulation, particularly when an elastomericencapsulation material such as liquid silicon rubber is used. Mold 600has a core plate 602 having a plateau 604 from which locating posts 606extend. On either side of plateau 604, core plate 602 has raised pads608 and holes 610. Raised pads 608 are illustratively oval shaped andextend the majority of the way between plateau 604 and edges.612 of coreplate 602. Mold 600 also has a cavity plate, not shown, that mates withcore plate 602 when mold 600 is closed. The cavity plate may also haveraised pads 608 and holes 610.

Raised pads 608 maintain coil 614 in centered spaced relation to asurface 620 of core plate 602 facilitating the flow of the encapsulatingmaterial 309 around the radial inner side 622 of coil 614. Holes 610result in compression tabs or projections 624 being formed inencapsulation 313 on the radial inner side 622 of field coil 304 and, ifprovided in the cavity plate of mold 600, on the radial outer side 628of field coil 304. (For continuity, reference number 622 is used toidentify the radial inner side of coil 614 and of field coil 304).Raised pads 608 form recesses 626 in the encapsulation 313 on radialinner side 622 of field coil 304 and, if provided in the cavity plate ofmold 600, on the radial outer side 628 of field coil 304. In addition toproviding spacing between coil 614 and core plate 602, and the cavityplate of the mold 600 if provided on the cavity plate, raised pads 608can also be used to thin out the walls of the encapsulation 313 thatencapsulates coil 614 of field coil 304. Compression tabs 624 providedadded areas of compression between field coil 304 and the pole pieces308 (compression tabs 624 on the radial inner side 622 of field coil304) and between the field coil 304 and the return path pieces 310(compression tabs 624 on the radial outer side 628 of field coil 304)when field coil 304 is assembled into stator 300 (FIG. 3). Compressiontabs 624 are dimensioned so that they are small compared to the overallarea of field coil 304 so that they provided added retention withoutsignificantly increasing the assembly interference forces when fieldcoil 304 is assembled with stator core pieces 306 (FIG. 3) to formstator 300 (FIG. 3).

With reference to FIGS. 6A–C, the molding of a field coil, such as fieldcoil 304 (FIGS. 3 and 6C), is described. The magnet wires 303 are woundin a coil 614 (FIG. 6B) having a predetermined shape, which isillustratively a section of a cylinder with a central open rectangularsection 616 (FIG. 6B), which is also the final shape of the field coil304 as can be seen from FIG. 6C. Coil 614 is placed in mold 600 so thatplateau 604 extends through central open rectangular section 616.Central open rectangular 616 of coil 614 is placed around locating posts606 when coil 614 is first placed in mold 600 which assist in properlylocating coil 614 on core plate 602 as coil 614 is being placed in mold600. Lead wires 302 are placed in slots 618 in core plate 602, only oneof which is shown in FIG. 6A. The cavity plate of mold 600 is closedover core plate 602 and the encapsulation material 309 (FIG. 3) injectedinto mold 600, encapsulating coil 614 to form field coil 304 with magnetwires 303 encapsulated in encapsulation 313 made of encapsulationmaterial 309.

Coil 614 of field coil 304 can be insulated by processes other thanencapsulation, such as applying a resin coating to them by using thetrickle resin process, applying an epoxy coat to them by dipping theformed coil 614 in a tank of epoxy, a powder coat process where heatedcoil windings cure powdered epoxy on the coil wires, applying anelectrically insulating foam to them, or winding insulating tape, suchas electrical insulating tape or epoxy tape, around them. In one type ofpowder coat process, heated coils are placed in a fluidized bed ofepoxy. When the coils are insulated by coating, the coating can beapplied to the coils before they are assembled in the stator or after.It should also be understood that the coils may be encapsulated orcoated to improve abrasion protection and tracking resistance and thecoils further insulated to provide insulation between the coils and thestator core pieces, such as with insulated slot liners or windinginsulating tape around the encapsulated or coated coils.

FIG. 7 shows a cross section of stator 400 (FIG. 4C) in which the fieldcoils 700 are insulated with a layer of insulating material 702 such asinsulating paper, electrical insulating tape, epoxy tape, or electricalinsulating foam. Insulating material 702 is wrapped around the coils offield coils 700 in the area abutting the field laminations, such asreturn path pieces 402 and pole pieces 404.

Such electrical insulating material, other than electrical insulatingfoam, is not compliant, so clearances must be left between theinsulating material 702 and the field laminations, such as return andpole pieces 402, 404. These clearances result in a degree of loosenessof field coils 700 in stator 400. To enhance product life anddurability, these clearances need to be eliminated, or at leastminimized. To do so, a compliant material 708 (FIG. 7B) is placedbetween the return path pieces 402 and the field coils 700. Compliantmaterial 708 may illustratively be a foam having a suitable temperaturerating. Compliant material 708 may also have adhesive on one or bothsides to facilitate retaining it in place during assembly of stator 400and improve retention of field coils 700 relative to return path pieces402.

If foam is used as electrically insulating material 702 or compliantmaterial 708, it may illustratively be thermally conductive to enhanceheat transfer. In this regard, it may contain fillers such as ceramicsto increase thermal conductively. Other types of fillers can be used,such as carbon which is cheaper than ceramic, if suitable for theelectrical design of the product.

Referring now to FIG. 8, a power tool 800 is shown. Power tool 800 isillustratively a hand-held power tool and is illustrated as a drill,however, any type of power tool may be used in accordance with thepresent invention. The power tool 800 includes a housing 802 whichsurrounds a motor 803. An activation member 804 is coupled with themotor and a power source 806, illustratively AC. The motor 803 iscoupled with an output 808 via a drivetrain 810. Output 808 includes achuck 812 having jaws 814 to retain a tool such as a drill bit (notshown). The motor 803 includes an armature 816 and a stator 818 made inaccordance with this invention, such as stator 300 or 400 (FIGS. 3 and4).

FIGS. 9–12 show an insulating sleeve 900 that can be used as theinsulating slot liner 322 (FIG. 3A) and in lieu of encapsulating thefield coils, such as field coils 1104 (FIG. 11). For convenience,insulating sleeve 900 will be described with reference to the stator 400of FIG. 4. Insulating sleeve 900 may illustratively be made of compliantmaterial, such as liquid silicon rubber, and may illustratively bemolded. Insulating sleeve 900 includes an outer section 902, innersection 904 and a bight section 906 bridging inner and outer sections904, 902 at one edge thereof. Locating or centering tabs 908 extend fromopposed ends 910 of bight section 906. An outer surface 912 of outersection 902 has laterally extending outwardly projecting compressionribs 914 formed thereon. A pocket 1000 (FIG. 10) may be formed in anouter surface 1002 of inner section 904 for receiving one of the poletips 420 of pole piece 404 (FIG. 4). Outer and inner sections 902, 904and bight section 906 of insulating sleeve 900 define a slot 916 inwhich one of sides 1102 of field coil 1104 (FIG. 11) is received.

The use of insulating sleeve 900 is now described. In assembling thestator 400, two insulating sleeves 900 are placed on field coil 1104with opposite sides 1102 (FIG. 11) of the field coil 1104 received inthe slots 916 of the respective insulating sleeves 900 to form fieldcoil/sleeve assembly 1100. The width of the outer section 902 of theinsulating sleeve 900 may illustratively be the same or preferablyslightly greater than the width of the side 1102 of the field coil 1104that is received in the slot 916 of the insulating sleeve 900 toinsulate the field coil 1104 from an inner surface of the return pathpiece 402 that is adjacent the side 1102 of the field coil 1104 when thefield coil 1104 is assembled in stator 400. The width of the innersection 904 of the insulating sleeve 900 may illustratively be the sameor preferably slightly greater than the width of the section of the poletip 420 of pole piece 404 that is adjacent the side of the field coil1104 when the field coil 1104 is assembled in stator 400 to insulate thefield coil from the surface of the pole tip 420 adjacent the side of thefield coil 1104.

A field coil/sleeve assembly 1100 is then placed over the neck 414 ofeach of the pole pieces 404 and the pole pieces 404 mated with thereturn path pieces 402. The pole tips 420 of each pole piece 404 arereceived in the pockets 1000 (FIG. 10) of the respective insulatingsleeves 900 disposed over the opposite sides 1102 of that field coil1104 to aid in retaining the field coil/sleeve assembly 1100 in place.Centering tabs 908 of the insulating sleeves 900 center the pole piece404 and the field coil/sleeve assembly 1100 with respect to each other.Compression ribs 914 compress against respective inner surfaces 434(FIG. 4B) of respective return path pieces 402 and aid in securing thefield coil/sleeve assembly in place in stator 400 so that the fieldcoil/sleeve assembly 1000 will not vibrate loose during operation of themotor in which it is used, such as in power tool 800.

Turning to FIG. 18, an insulating sleeve 1800 that is a variation ofinsulating sleeve 900 is shown. Insulating sleeve 1800 is also made ofcomplaint material, such as silicon rubber, but is extruded instead ofmolded. Insulating sleeve 1800 includes an outer section 1802, an innersection 1804 and a bight section 1806 bridging inner and outer sections1804, 1802 at one edge thereof. An outer surface 1808 of outer section1802 has outwardly projecting compression ribs 1810 formed thereon thatextend across outer section 1802. Outer and inner sections 1802, 1804and bight section 1806 define a slot 1812 in which one side of a fieldcoil, such as field coil 1104 (FIG. 11) is received: Compression ribs1810 allow tuning adjustments in the tool used to extrude insulatingsleeve 1800 so that the retention force on the field coil, such as fieldcoil 1104, when it is assembled as part of a stator such as stator 400can be optimized.

With reference to FIG. 5E, edges 526 of radially outer section 521 ofpole tip section 522 are recessed and have a radius at 530. However,edges 526 are not formed to include lips 528 (FIG. 5D) so that aradially extending outer surface 532 of radially outer section 521 ofpole tip portion 522 presents a smooth wall free of detents, lips or thelike. This improves assembly when the field coils are insulated withcompliant insulating sleeve 900 and insulating slots liners made ofpaper such as embodiments of insulating slot liners 322. (FIG. 3A), 1300and 1600 (described below.) The radius 530 and the smooth wall presentedby surface 532 helps prevent displacing the insulating sleeve 900 andinsulating slot liners 1300, 1600 from their proper position around thefield coils.

As mentioned, insulating sleeve 900 may illustratively be made ofcompliant material, such as liquid silicon rubber, and mayillustratively be used in lieu of encapsulating the field coils. Thisprovides the benefit of not having to insert mold the field coils withan encapsulant. Insulating sleeves 900 can be molded separately at arate that applicants expect will be much faster than the rate at whichthe field coils can be wound and the mold(s) used to mold the insulatingsleeves will likely be able to have more cavities than the mold(s) usedto insert mold the field coils.

FIGS. 13–15 show an insulating slot liner 1300 in accordance with anembodiment of the invention that can be used as insulating slot liner322 (FIG. 3A) and in lieu of encapsulating the field coils. Insulatingslot liner 1300 includes a substrate 1302 made of insulative material,such as insulating paper, insulating plastic film, or the like having anouter section 1301 and an inner section 1303. Illustrative materials ofwhich substrate 1302 can be made include various grades of Nomex® paperor tape, polyester/glass fiber, polyester/rag, Nomex®/polyester, orpolyester/Dacron® laminates. An inner adhesive strip 1304 is disposed onan inner surface 1306 of outer section 1301 of substrate 1302 and anouter adhesive strip 1308 is disposed on an outer surface 1310 of innersection 1303 of substrate 1302. An outer surface 1404 (FIG. 14) of outersection 1301 may also have an adhesive strip (not shown) disposedthereon as may an inner surface 1406 of inner section 1303. Inner andouter adhesive strips 1304, 1308 may illustratively include non-stickoverhanging cover strips 1400 (FIG. 14) that can be easily removed frominner and outer adhesive strips 1304, 1308 during assembly. One or bothof opposed upper and lower edges 1312 of substrate 1302 mayillustratively be folded over cuffed edges.

Insulating slot liner 1300 may illustratively be “C” or “U” shaped andmay illustratively be preformed so that it fits the contours of thefield coils, such as field coils 614, and radially outer surfaces 1500(FIG. 15) of pole tips 420 of pole pieces 404 of stator 400 that abutfield coils 614 and inner surfaces 1502 of return path pieces 402. Thisaids in adhesive retention such as between inner adhesive strip 1304 andfield coil 614 and/or between outer adhesive strips 1308 and thesurfaces 1500 of pole tips 420 of pole pieces 404. This also aids inassembly. Insulating slot liner 1300 may illustratively be sized so thata distal edge 1505 (FIG. 15) of outer section 1301 extends beyond adistal edge 1506 of field coil 614 and a distal edge 1508 of innersection 1303 extends beyond an outer edge 1510 of pole tip 420. In a 59mm. O.D. stator, this distance is illustratively a minimum of 2 mm.Cuffed edge(s) 1312 of substrate 1302 extend over axial edge(s) 436(FIG. 4B) of return path piece 402 and axial edge(s) 438 (FIG. 4A) ofpole piece 404 to locate insulating slot liner 1300 on return path piece402 and pole piece 404 and, when both opposed edges 1312 of substrate1302 are cuffed, to capture insulating slot liner 1300 on return pathpiece 402 and pole piece 404.

The use of insulating slot liners 1300 is now described. In assemblingthe stator 400, cover strips 1400 are removed from the inner adhesivestrips 1304 of two insulating slot liners 1300 which are then placed onfield coil 614 with the opposites sides of the field coil 614 receivedin respective ones of the insulating slot liners 1300. If an adhesivestrip is provided on inner surface 1406 of inner section 1303, its coverstrip is removed before placing the insulating slot liner 1300 over theside of field coil 614. Inner adhesive strip 1304 secures the insulatingslot liner 1300 to the side of the field coil 614 over which theinsulating slot liner 1300 was placed. The cover strips 1400 are thenremoved from outer adhesive strips 1308 of the insulating slot liners1300 and field coil/insulating slot liner assembly 1514 (FIG. 15) placedover the neck 414 of a pole piece 404, bringing the outer adhesivestrips 1308 of the insulating slot liner 1300 into contact with thesurfaces 1500 of the pole tips 420 of the pole piece 404 so that theadhesive on the outer adhesive strips 1308 contacts the surfaces 1504 ofthe pole tips 420. The return path pieces 402 are then mated with thepole pieces 404. If an adhesive strip is provided on the outer surface1404 of outer section 1301 of insulating slot liner 1300, its coverstrip is removed before the return path piece 402 that will abut thatinsulating slot liner 1300 is mated to the pole piece 404. It should beunderstood that while only one insulating slot liner 1300 is shown inFIG. 15, all of field coils 614 would be insulated with insulating slotliners 1300, illustratively, two insulating slot liners 1300 for eachfield coil 614.

Inner adhesive strip 1304 may illustratively be a pliable adhesivestrip, such as a foam or gel strip ranging from 0.001″ to 0.250″ inthickness, to take up clearances and fill into component contours offield coil 614 to provide a robust retention force. Outer adhesive strip1308 may also be a pliable adhesive strip.

Outer adhesive strip 1308 may illustratively be sized so that there is agap between its edges and the edges of substrate 1302, shownrepresentatively at 1316. That is, outer adhesive strip 1308 is smallerthan the outer surface 1310 on which it is disposed. By having a gapbetween the edges of substrate 1302 and outer adhesive strip 1308, thatis, sizing outer adhesive strip 1308 so that it is smaller than theouter surface 1310 on which it is disposed, the adhesive on outeradhesive strip is completely covered by inner surface 1502 of returnpath piece 402 when insulating slot liner 1300 is assembled in stator400. This minimizes or eliminates any dust or chips contacting theadhesive on outer adhesive strip 1308 and being retained thereon.Similarly, inner adhesive strip 1304 may illustratively be sized so thatit is smaller than the inner surface 1306 of substrate 1302 on which itis disposed. It should be understood that the insulating slot liner 1300could have multiple inner and outer adhesive strips 1304,1308.

The inner and outer adhesive strips 1304, 1308 of the insulating slotliners 1300 serve three purposes. They retain the field coils 614 to thereturn path pieces 402 and pole pieces 404 and prevent slippage betweenfield coils 614 and the return path pieces 402 and pole pieces 404. Theyact as a secondary support to hold together the windings of field coil614. They also act as a secondary support to hold together the returnpath piece 402 and the pole piece 404.

The thickness of the substrate 1302 of insulating slot liner 1300 mayillustratively be optimized to take up clearances thus keeping theassembly of the field coils 614 and the return path and pole pieces 402,404 tight and keeping pressure on inner and outer adhesive strips 1304,1308 as they contact field coils 614 and the inner surfaces 1502 ofreturn path pieces 402, respectively. In a 59 mm O.D. stator 400, theoptimum thickness of substrate 1302 is in the range of 0.002″ to 0.030″.The distal edge 1505 of outer section 1301 may also be folded over asshown at 1402 in FIG. 14. Doing so helps take up clearances, increasesthe interference in a localized area for a tight fit in that localizedarea. It may also allow a thinner, better conforming, lower cost paperto be used for substrate 1302.

Certain materials, such as some types of insulated paper, that can beused for substrate 1302, have a smooth surface on one side and a roughsurface on the other side. For these materials, insulating slot liner1300 may illustratively be formed so that the smooth surface is theouter surface of substrate 1302 that contacts the surfaces 1500 of poletips 420 and inner surfaces 1502 of return path pieces 402 to facilitateassembly.

As shown in FIG. 15, field coil 614 could in an alternative embodimentbe insulated with a full wrap of insulated material, such as insulatedpaper, as shown in phantom at 15.12. This reduces the likelihood of theinsulated paper curling up into the armature of the motor in whichstator 400 is used and prevents slippage of the insulated paper duringassembly.

FIGS. 16A and 16B show an insulating slot liner 1600 which is avariation of insulating slot liner 1300. Like elements will beidentified with the same reference numbers and only the differences willbe described. Insulating slot liner 1600 includes compliant material1602 disposed on inner and outer surfaces 1406, 1310 of inner section1303 and inner and outer surfaces 1306, 1404 of outer section 1301 ofsubstrate 1302. The compliant material 1602 provide an interferencebetween the substrate 1302 of the insulating slot liner 1600, the fieldcoil, such as field coil 614 (FIG. 15), and the return path pieces 402and pole pieces 404. It should be understood that compliant material1602 can be disposed on one as opposed to both of the inner and outersurfaces 1306, 1404 of outer section 1301 of substrate 1302 and on oneas opposed to both of the inner and outer surfaces 1406, 1310 of innersection 1303 of substrate 1302. It should also be understood thatcompliant material 1602 can be strips of complaint material, beads orother shapes. It should further be understood that complaint material1602 can be any suitable complaint material, such as compliant polymerssuch as silicon, resins, foams or epoxies.

Alternatively or in addition to encapsulating the field coils and orusing insulating slot liners, the stator core pieces 306 or appropriateportions of the stator core pieces can be encapsulated or covered withan encapsulating or coating material, such as thermoplastics andthermosets, which may illustratively be thermally conductive or not. Byway of example and not of limitation, the stator core pieces 306 (orappropriate portions of them) can be covered with an epoxy coating thatis either sprayed on or applied using an electrostatic coating process.With reference to FIG. 19, a layer 1900 of insulation is applied tosurfaces 1902 of pole tip portion 522 of pole piece 404 and to radiallyinner facing surfaces 1904 of return path pieces 402 (only one of whichis shown in FIG. 19).

Referring to FIGS. 20 and 21, an insulating slot liner 2000 that is avariation of insulating sleeve 1300 (FIG. 13) is shown. Insulating slotliner 2000 is made of a layer of insulation material, such as one of theabove referenced insulation papers, having both sides or surfaces coatedwith a thin layer of a B-stage thermosetting adhesive, such asVonRolllsola 6001 (phenolic) or 6351 (epoxy). A B-stage thermosettingadhesive is one that is dry to the touch and not tacky and is in a stateto be cured by the application of heat. An insulating slot liner 2000 iswrapped around each portion of a field coil that is disposed between apole piece and a return path piece mated to that pole piece. Insulatingslot liner 2000 is illustratively formed with creases to contour aroundthe field coil. Additionally, for lower temperature applications, athermoplastic adhesive could be used, such as VonRolllsola HS2400.Moreover, pre-laminated films with adhesives could also be used, such as3M bonding film 583 or 588 (heat or solvent cure), or 3M ENPE-365 (UVlight cure). The film containing the resin is itself adhered to theinsulation paper used for the slot liner.

In assembly, insulating slot liner 2000 is wrapped around theappropriate portion of the field coil, such as field coil 2100 (FIG.21), and secured with a thin tape, such as 0.025 mm thick acrylicadhesive tape, to form insulated field coil 2102. The insulated fieldcoil 2102 is then placed over the neck 414 of a pole piece 404 (FIG. 4).Preferably, there will be enough pressure between the insulating slotliner 2000 and pole piece 404 to hold the two together during assemblyof stator 400. If not, a temporary adhesive may be used, such as thindouble-sided taped, one or two part adhesives, and UV light cureadhesives.

The thickness of the material, such as insulating paper, used forinsulating slot liner 2000 is chosen so that there is a slight pressurebetween field coil 2100, the insulating slot liner 2000, and the returnpath pieces 402 and the pole pieces 404 after final assembly. This willhold the field coil 2100 in the proper position until the B-stageadhesive is activated and cured. If there is not sufficient pressure, atemporary adhesive can be used until the B-stage adhesive is cured. TheB-stage adhesive on both sides of the material used for insulating slotliner 2000 adheres to both the field coil 2100 and the return pathpieces 402 and the pole pieces 404, and secures them to each other. Thisfacilitates the motor in which the stator 400 is used withstanding heavyvibrations that are seen in some motor/power tool applications. TheB-stage adhesive also acts to bond the individual laminations of thereturn path pieces 402 and pole pieces 404 together.

FIG. 22 shows a field (stator) made in accordance with this inventionutilizing the insulated field coils 2102. Elements in common with thosedescribed above with reference to previously discussed figures areidentified with the same reference numerals used for those elements inthose figures. In the illustrative embodiment of FIG. 22, after fieldcoils 2102 are placed on the necks of pole pieces 404 and pole pieces404 mated with return path pieces 402, field coils 2102 are coated withepoxy using one of the processes described above. Illustratively, fieldcoils 2102 are coated with epoxy by placing the field 2102 in afluidized bed of epoxy and heating field coils 2102, such as by runningelectrical current through them.

The description of the invention is merely exemplary in nature and,thus, variations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the spirit and scope of theinvention.

1. An electric motor, comprising: a. a multi-piece stator having aplurality of pole pieces with a plurality of return path pieces mated toeach of the pole pieces and a plurality of field coils; i. each returnpath piece having opposed ends with a projection extending from eachend; ii. each pole piece having a neck with opposed receiving pocketstherein between opposed outer fingers of a radial outer end of the neckand opposite sides of a radially outer section of a pole tip section ofthe pole piece, each opposed receiving pocket having one of theprojections of one of the return oath pieces received therein, each polepiece secured to the return path pieces mated to the pole piece bydeformation of the opposed outer fingers of the radial outer end of theneck of the pole piece against the projections of those return oathpieces, the fingers of the radial outer end of the neck of each polepiece having radially inwardly extending projections and the projectionsof the return path pieces have recesses that are distally spaced fromjunctions of the projections of the return path pieces and the ends ofthe return path pieces, the radially inwardly extending projections ofthe fingers of the radial outer end of the neck of each pole piecereceived in the recesses of the return path pieces when the fingers aredeformed against the projections of the return path pieces received inthe opposed receiving pockets of the pole pieces to form mating detectsthat mechanically lock the pole piece and the return path piecestogether, the mating detents distally spaced from the junctions of theends of the return path pieces and the projections of the return oathpieces to increase a critical length of the pole piece and return pathpieces mated to the pole piece; iii. at least one of the field coilsdisposed around each pole piece between the pole tip section of the polepiece and the return path pieces mated to the pole piece; and b. anarmature received in the stator.
 2. The electric motor of claim 1wherein each return path piece is also welded to each pole piece towhich it is mated.
 3. An electric motor, comprising: a. a multi-piecestator having a plurality of pole pieces with a plurality of return pathpieces mated to each of the pole pieces and a plurality of field coils;i. each return oath piece having opposed ends with a projectionextending from each end; ii. each pole piece having a neck with opposedreceiving pockets therein between opposed outer fingers of a radialouter end of the neck and opposite sides of a radially outer section ofa pole tip section of the pole piece, each opposed receiving pockethaving one of the projections of one of the return path pieces receivedtherein, each pole piece secured to the return oath pieces mated to thepole piece by deformation of the opposed outer fingers of the radialouter end of the neck of the pole piece against the projections of thosereturn path pieces; iii. at least one of the field coils disposed aroundeach pole piece between the pole tip section of the pole piece and thereturn path pieces mated to the pole piece; iv. the opposite sides ofthe radially outer section of the pole tip section of each pole piecehaving circumferentially and radially outer edges that are recessed andhave a radius to facilitate placement of the field coils on the pole andb. an armature received in the stator.
 4. The electric motor of claim 3wherein the circumferentially and radially outer edges of the pole tipsection of each pole piece project outward to provide lips that provideretention of the field coils disposed on the pole pieces.
 5. An electricmotor, comprising: a. a multi-piece stator having a plurality of polepieces with a plurality of return path pieces mated to each of the polepieces and a plurality of field coils; i. each return path piece havingopposed ends with a projection extending from each end; ii. each polepiece having a neck with opposed receiving pockets therein and a poletip section extending radially inwardly from the neck, each opposedreceiving pocket having one of the projections of one of the return pathpieces received therein; iii. each pole path piece secured to the returnpath pieces mated to the pole piece by welding; iv. at least one of thefield coils disposed around each pole piece between the pole tip sectionof the pole piece and the return path pieces mated to the pole piece; v.each pole tip section having circumferentially and radially outer edgesthat are recessed and have a radius to facilitate placement of the filedcoils on the pole pieces; and b. an armature received in the stator. 6.A hand-held power tool, comprising: a. a housing surrounding an electricmotor, the electric motor including: a multi-piece stator having aplurality of pole pieces with a plurality of return path pieces mated toeach of the pole pieces and a plurality of field coils; each return pathpiece having opposed ends with a projection extending from each end;each pole piece having a neck with opposed receiving pockets thereinbetween opposed outer fingers of a radial outer end of the neck andopposite sides of a radially outer section of a pole tip section of thecole piece, each opposed receiving pocket having one of the projectionsof one of the return path pieces received therein, each pole piecesecured to the return path pieces mated to the pole piece by deformationof the opposed outer fingers of the radial outer end of the neck of thepole piece against the projections of those return path pieces, thefingers of the radial outer end of the neck of each pole piece havingradially inwardly extending projections and the projections of thereturn path pieces have recesses that are distally spaced from junctionsof the projections of the return path pieces and the ends of the returnpath pieces, the radially inwardly extending projections of the fingersof the radial outer end of the neck of each pole piece received in therecesses of the return path pieces when the fingers are deformed againstthe projections of the return path pieces received in the opposedreceiving pockets of the pole pieces to form mating detents thatmechanically lock the pole piece and the return path pieces together,the mating detents distally spaced from the junctions of the ends of thereturn path pieces and the projections of the return path pieces toincrease a critical length of the pole piece and return path piecesmated to the pole piece; at least one of the field coils disposed aroundeach pole piece between the pole tip section of the pole piece and thereturn path pieces mated to the pole piece; ii. an armature received inthe stator; and b. a drive train coupled to the motor.
 7. The power toolof claim 6 wherein each return path piece is also welded to each polepiece mated to the return path piece.
 8. A hand-held power tool,comprising: a. a housing surrounding an electric motor, the electricmotor including: a multi-piece stator having a plurality of pole pieceswith a plurality of return path pieces mated to each of the pole piecesand a plurality of field coils; each return path piece having opposedends with a projection extending from each end; each pole piece having aneck with opposed receiving pockets therein between opposed outerfingers of a radial outer end of the neck and opposite sides of aradially outer section of a pole tip section of the pole piece, eachopposed receiving pocket having one of the projections of one of thereturn path pieces received therein, each pole piece secured to thereturn oath pieces mated to the pole piece by deformation of the opposedouter fingers of the radial outer end of the neck of the pole pieceagainst the projections of those return path pieces; at least one of thefield coils disposed around each pole piece between the pole tip sectionof the pole piece and the return path pieces mated to the pole piece;the opposite sides of the radially outer section of the pole tip sectionof each pole piece having circumferentially and radially outer edgesthat are recessed and have a radius to facilitate placement of the fieldcoils on the pole pieces; ii. an armature received in the stator; and b.a drive train coupled to the motor.
 9. A power tool, comprising a. ahousing surrounding an electric motor, the electric motor including: i.a multi-piece stator having a plurality of pole pieces, a plurality offield coils and a plurality of return path pieces, a plurality of thereturn path pieces mated to each of the pole pieces; each pole piecehaving a neck with opposed receiving pockets therein and a pole tipsection extending radially inwardly from the neck, each opposedreceiving pocket having one of the projections of one of the return pathpieces received therein; each pole oath piece secured to the return pathpieces mated to the pole piece by welding; at least one of the fieldcoils disposed around each pole piece between the pole tip section ofthe pole piece and the return path pieces mated to the pole piece; eachpole tip section having circumferentially and radially outer edges thatare recessed and have a radius to facilitate placement of the filedcoils on the pole pieces by allowing the field coils to slide morefreely onto the pole pieces when placed onto the pole pieces; ii. anarmature received in the stator; and b. a drive train coupled to themotor.